1. Field of the Invention
This invention relates generally to a heavy duty industrial vacuum unit and more particularly to pressure relieving means for relieving internal pressure within the unit.
2. Description of the Prior Art
In industrial vacuum units a positive pressure can exist therein after the vacuum unit is turned off. This problem occurs because residual internal vacuum pressures often result from clogged hoses, and this can cause the vacuum-creating compressor to reverse and run backwards. While a temporary reversal of the compressor is not undesirable, in that the associated reversed air flow cleans internal filters, the continued operation in reverse can create excessive positive pressures which are undesirable.
More specifically, when a vacuum unit is turned off, a residual negative pressure can exist within the unit if the vacuum hose is filled with debris or otherwise blocked, thus preventing relief of the internal negative pressure through the vacuum hose. If the hose is blocked when the compressor is turned off, the residual negative pressure will remain in the vacuum unit. This negative pressure can draw outside air backward through the compressor and thus cause the compressor to run in a reverse direction until the negative pressure is eliminated. However, once the compressor begins running in reverse it sometimes reaches high speeds and momentum which causes the compressor to overrun and continue running after the negative pressure has been eliminated.
Hence, a condition is created whereby the inside of the vacuum unit goes from a negative pressure to a brief interval of neutral pressure, wherein the inside and outside air pressures are matched, and then, by the momentum effect of the compressor, to a condition in which positive pressure can begin to build up within the unit. If there is no relief for this newly created positive pressure it is possible that the debris trapped within the hose or at the mouth of the hose could be rapidly discharged and/or dissipated, creating a potentially dangerous situation to personnel in the adjacent area.